In the related art, an air intake device including a valve, which can be turned to switch between flow paths of an air intake port, is known (for example, refer to JP 2010-1847A (Reference 1)).
Reference 1 discloses a variable air intake device including an air intake port, and a valve that switches the flow path of the air intake port between a short port, the passage length of which is short, and a long port, the passage length of which is long. The valve of the variable air intake device includes a rectangular valve body including rounded corners, and a seal lip that is joined to a side end portion of the rectangular valve body and is made of rubber. Specifically, the valve body is formed into a rectangular shape including four sides which are straight except for the rounded corners. A side end portion of the seal lip is provided with a contact portion that is formed to extend from the vicinity of a side end portion of the valve toward an opening direction of the valve, and is in contact with an inner wall surface of the air intake port in a state where the contact portion is elastically deformed. The contact portion comes into contact with the inner wall surface of the air intake port such that a gap between the valve and the air intake port is sealed. The contact portion (side end portion) of the seal lip is formed straight except for a portion corresponding to the corners of the valve such that the contact portion corresponds to the rectangular valve body including the rounded corners.
As a result of in-depth study, the inventors have found that the variable air intake device disclosed in Reference 1 has a problem in that external force caused by the flow of intake air or the like is applied to the contact portion of the seal lip, and then the contact portion is deformed. As a result, due to insufficient contact between the deformed contact portion and the air intake port, in the air intake device, the gap between the air intake port and the valve is not sufficiently sealed.